Method and apparatus for manufacturing slabs with veined effect

ABSTRACT

During the manufacture of slabs with a veined effect a liquid or powder coloring agent is deposited on the surface of a thin layer of starting mixture by means of at least one dispensing device ( 40 ) and the resultant mixture is supplied, falling freely, from one end of an extractor belt ( 30 ) forming the bottom of a mixture metering/distributor unit, following which the mixture is transferred, falling freely, onto a temporary molding support ( 14 ). This results in the production of slabs provided with veining extending through the entire thickness of the slabs and also visible along the whole edge of the slab, even after it has been machined.

RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national stage filing fromInternational Application No. PCT/EP2008/058682 filed Jul. 4, 2008,which claims priority to Italian Application No. TV2007A000126, filedJul. 16, 2007, the teachings of which are incorporated herein byreference.

The present invention relates to the manufacture of conglomerate stoneslabs obtained from mixtures consisting of granules of stone and/orstone-like material and a bonding agent, and more specifically to themanufacture of slabs of this type which have particular colouringeffects, such as so-called veining, intended to imitate as closely aspossible natural stone materials.

More specifically the invention relates to a method and an apparatus forproducing the slabs in question. In the description which followsreference will be made to the production of slabs with a veined effect,it being understood that reference thereto is made solely by way of anon-limiting example.

For many years so-called Bretonstone slabs have been known, this namereferring to a particular manufacturing technology which essentiallyenvisages the preparation of one or more starting mixtures comprisinggranules of stone and/or stone-like material with a specific particlesize distribution and a bonding agent which made be of an inorganicnature (such as cement) or a synthetic resin which can be hardened (bythe action of heat and/or a catalyst).

The starting mixture is distributed in the form of a layer ofpredetermined thickness on a temporary moulding support (such as aconveyor belt or a tray mould) and then subjected, for a predefinedperiod of time and under a vacuum of given intensity, to the action of apress while a vibratory movement of prechosen frequency is applied tothe press ram.

The resultant rough-formed slab is then transferred to the hardeningstage using procedures which depend on the nature of the bonding agent.

In the continuation of the present description reference to Bretonstoneslabs and/or the Bretonstone method is understood as meaning slabsobtained with the method described above.

According to an already known method for manufacturing Bretonstone slabswith a veined effect, after the step involving deposition of thestarting mixture on the temporary support, colouring agent isdistributed in an irregular manner on the surface of the layer ofmixture and then the colouring agent is mixed up with the mixture usinga spiked tool so that the colouring agent penetrates into the thicknessof the mixture to a depth such that the finished slab, after the usualsizing and polishing operations, has veining similar to that of thenatural stone from which the granules used in the mixture are obtained.

For further details regarding this method and the associated apparatusreference should be made to the patent IT-A-1,328,246 (corresponding toWO-A-03/027042) in the name of the same applicant, herein incorporatedby reference.

This method is useful solely in the case where the finished slab mustnot be used such that its side edges are visible.

In fact, it has been found that, no matter how effectively mixing up ofthe colouring agent may be performed by means of the spiked tool, thecolouring agent penetrates into the thickness of the mixture—and cantherefore be seen in the finished slab—only over a section of a fewmillimeters, corresponding to not more than half the thickness of thefinished slab.

There exist, however, certain uses of the finished slabs where the edgeor side of the slab also remains visible (as, for example, in the caseof so-called kitchen or bathroom tops) and, after polishing, the veiningcan be noted only in a thickness of a few millimeters from the topsurface, while it is absent in the remainder of the edge or side to thedetriment of the aesthetic characteristics of the slab laid.

According to an alternative solution, also known, for obtainingBretonstone slabs with a veined effect, the mixture is distributed onthe moulding support by means of a weighing type distributor unit withthe characteristic features described in the patent IT-A-1,335,533(corresponding to WO-A-2004/039547), herein incorporated by reference.

In this case, the starting mixture, before being loaded into themetering unit, is made to pass underneath devices which apply liquid orpowder colouring or pigments agents onto its surface.

Since the mixture is loaded into the metering unit, falling freely, andthen conveyed to the outlet for discharging onto the moulding support,it undergoes a certain degree of remixing which in turn results, on theone hand, in a substantial shortening of the veining and, on the otherhand, in a not insignificant diffusion of the pigment in the mass of themixture which is therefore at least partly coloured throughout the mass.

Another technology known for many years and aimed at the manufacture ofslabs designed for internal and external cladding of buildings as wellas the manufacture of articles similar to ceramic articles is one wheregranules of stone, stone-like or ceramic material, preferably in theform of sand, with a suitable particle size distribution, are mixed withthe components normally used for the manufacture of ceramic materials,usually in powder form, and consisting mainly of clay or kaolin.

The resultant mixture is wetted with a bonding agent, which may besodium silicate in aqueous form or a mixture of silicasol and polyvinylalcohol.

With this starting mixture a layer of predetermined thickness is formedon a temporary support which is then subject to a vibrocompression step,resulting in a rough-formed slab.

The slab, after a drying step, in order to remove the water present inthe mixture, undergoes a baking step at a high temperature (in theregion of 1200° C.).

Below this technology, the associated method and the resultant slabswill be referred to by the generic name of “Lapitech”.

This type of slab and technology is also affected by the same problemalready mentioned with regard to the Bretonstone slabs.

It is therefore desirable to provide a method and a correspondingapparatus for manufacturing slabs of the Bretonstone or Lapitech type inwhich the slabs have coloured veining with a length comparable to thatof standard natural stone and this veining is visible throughout thethickness and therefore along the entire edge of the finished slabs.

This object is achieved with a method for manufacturing slabs in which:

-   -   at least one starting mixture comprising at least one granular        product comprising stone or stone-like or ceramic material with        a specific particle size distribution and a hardening bonding        agent is prepared;    -   said at least one mixture is loaded into a metering/distributor        unit comprising:    -   a hopper with a top mouth for loading the mixture and a bottom        opening for discharging the said mixture;    -   an extractor belt which forms the bottom wall of said hopper;    -   the mixture discharged from the bottom opening of said hopper is        transferred by means of said extractor belt so that, falling        freely from said belt, it is distributed in the form of a layer        of predetermined thickness on a temporary moulding support        positioned at a lower level than said extractor belt;    -   the layer of mixed formed on said temporary support is subjected        to vibrocompression so as to obtain a rough-formed slab;    -   after a drying step, where applicable, said rough-formed slab is        transferred into a hardening station,

the method being characterized in that at least one colouring orpigmenting agent is distributed on the surface of the mixture beingtransferred by means of said extractor belt before the mixture isdistributed, falling freely, onto said temporary moulding support.

Advantageously, the metering/distributor unit used in said method isthat described and illustrated in Italian patent application No. TV2004A000118 (corresponding to WO-A-2006/045728), herein incorporated byreference.

In the case where Bretonstone slabs are manufactured, the methodaccording to the present invention envisages that: the bonding agentcontained in the at least one starting mixture may be of an inorganicnature (such as cement) or a synthetic resin which can be hardened (bythe action of heat and/or a catalyst); the layer formed on saidtemporary moulding support is subjected, for a predefined period of timeand under a vacuum of given intensity, to the action of a press, while avibratory movement of prechosen frequency is applied to the press ram;the resultant rough-formed slab is subjected to the hardening step usingprocedures which depend on the nature of the bonding agent.

In the case where Lapitech slabs are manufactured, where said startingmixture (as already mentioned) comprises, in addition to the granules ofstone, stone-like or ceramic material with a prechosen particle size, inparticular in the form of sand, also materials known per se for themanufacture of ceramic materials, such as clay and kaolin in powder formand an agent chosen from sodium silicate and silicasol together withpolyvinyl alcohol, the rough-formed slab resulting from thevibrocompression step is subjected to a drying step and then ahigh-temperature baking step such that the clay or kaolin forms abonding matrix for the abovementioned granules.

In the preferred embodiment of the invention said at least one colouringagent is distributed on the surface of the mixture in a non-uniformmanner.

In turn the apparatus according to the invention is that described inthe already cited Italian patent application No. TV2004A000118, exceptthat it comprises as a characterizing aspect at least one device fordispensing colouring or pigmenting agent positioned at the downstreamend of the extractor belt forming the bottom of the already mentionedhopper so as to dispense said colouring agent onto the surface of thelayer of mixture transported by means of said extractor belt towards theposition where it falls freely onto the said temporary moulding support.

It has been established that with the method and the apparatus accordingto the present invention the colouring agent is distributed randomly andnot uniformly within the mass mixture, which falls into the temporarysupport producing the aforementioned veining which affects the entirethickness of the finished slab.

The colouring or pigmenting agent may be in solid form (preferably a drypowder) or liquid form and may be supplemented with or replaced bycolouring or reflective granules which result in very attractive specialeffects in the finished product and throughout its thickness.

Considering now specifically the colouring agent dispensing deviceassociated with the abovementioned apparatus, it may comprise aplurality of devices, namely one for each colouring agent, which arecontrolled independently of each other as regards the start and end ofthe dispensing operation, which may take place continuously orintermittently.

In the case where there is a plurality of dispensing devices, they maybe mounted transversely with respect to the direction of feeding of theextractor belt which transports the layer of mixture discharged by themetering/distributor unit, so as to cover the entire width of themixture layer.

Alternatively, it is possible to envisage a smaller number of dispensingdevices mounted on a cross-member fixed at the top and transversely withrespect to the extractor belt for the layer of mixture and movable alongthe said cross-member.

The invention will now be described with regard to the accompanyingdrawings which show, by way of a non-limiting example, two variations ofembodiment of the apparatus according to the invention.

More specifically:

FIG. 1 is a front view of the apparatus provided with a plurality ofunits for dispensing colouring or pigmenting agents according to theinvention;

FIG. 2 is a partially sectioned side view of the apparatus according toFIG. 1;

FIG. 3 is a side view of solely the mixture metering/distributor unitequipped with a device for dispensing colouring agent in powder formaccording to a first embodiment of the invention which is also visiblein FIG. 2;

FIG. 4 is a view similar to that of FIG. 3 of a device for dispensingliquid colouring agent according to a second embodiment of the inventionwhich is also visible in FIG. 1;

FIGS. 5 and 6 are axonometric views of products which can be obtainedwith the present invention.

FIGS. 1 and 2 show an apparatus according to the present invention fordistributing, in the form of a thin layer, on a support used in a plantfor producing stone articles, a mixture based on agglomerate stone orceramic material, to which colouring substances are added depending onthe predetermined aesthetic effects.

In brief, the apparatus comprises a frame 10 which supports a surface 12on which a temporary moulding support 14 is placed for each operatingcycle, on which support a layer of mixture 18, supplied by ametering/distributor device denoted overall by the referenced above 20,is deposited in a free-falling manner.

The mixture distributor 20 in turn comprises a hopper 22 with a topmouth 24 for loading fresh mixture, a shaped or conveying wall 26 with aprofile curved towards the inside of the hopper 22 and a mixturedischarge opening 28 at the end of said shaped wall 26.

An extractor belt 30, positioned underneath said hopper 22, forms withits upper surface 30 the bottom of said hopper.

The belt 30 is used to convey and deposit a uniform layer of saidmixture, after it has flowed inside the hopper 22 and passed out throughsaid discharge opening 28, on said temporary support 14 which ispositioned at a lower level than said extractor belt. At the same time arelative movement of said hopper 22 and said support 14 is maintained sothat the layer of mixture distributed on said support is uniform.

In order to ensure the relative movement of hopper 22 and temporarysupport 14, the metering/distributor device 20 is mounted on a carriagedenoted overall by the reference number 34 and movable by means ofroller wheels parallel to the surface 12 of the apparatus.

From FIG. 1 it can be readily understood how the distribution andmetering hopper 22, the extractor belt 30 as well as the mixturedischarge opening 28 extend substantially over the entire width of thesurface 12 so that the resultant product is a slab which has notabledimensions not only lengthwise but also transversely. In this connectionit is worth noting that the slabs which can be obtained with thistechnology may have and in reality also have widths greater than 1.5meters and lengths greater than 3.3 meters.

For further details regarding this apparatus reference should be made tothe already mentioned Italian patent application No. TV2004A000118.

According to the invention, at least one device for dispensing colouringagent, denoted by the general reference number 40, is positioned at thedownstream end of the extractor belt 30, preferably downstream of thedischarge opening 28 of the hopper 22.

In this connection it should be noted that the colouring agent may bedispensed at any point on the upper surface 32 of the extractor belt 30,except for the zone immediately underneath the hopper 22.

In particular, in accordance with the embodiment shown in FIGS. 1 and 4,at the downstream end zone of the extractor belt 30, the carriage 34has, mounted thereon, a support structure comprising a cross-member 36with, fixed thereto, a plurality of devices for dispensing colouringagent—denoted by the reference numbers 40 (a-m), respectively—each ofwhich has a nozzle intended to emit a continuous or discontinuous jet ofcolouring agent (which, as ready mentioned, may be liquid or in the formof dry powder) which strikes a strip of the layer of mixture depositedon the tray mould, so as to cover overall the entire width of themixture.

As regards the structure of the colouring agent dispensers, it ispreferably that described in the aforementioned Italian patentapplication TV2004A000118 and illustrated in FIGS. 2 and 3 thereof.

The surface of the mixture, before leaving the extractor belt 30, istherefore sprinkled with colouring material in a manner which depends onthe operating mode of the dispensing nozzle. In fact, if the dispensingnozzle is operated intermittently and at irregular time intervals, it isevident that the distribution of colouring agent on the surface of themixture will not be homogeneous and pre-ordered.

Since the mixture with colouring agent is then transferred by means of afree-falling action onto the temporary moulding support and since themixture when falling produces coloured lumps on the surface, thecolouring agent, without uniformly colouring the mixture, is able toproduce during the subsequent vibrocompression step colouring effectswhich affect the entire thickness of the manufactured article, similarto the veining of natural stones.

If, on the other hand, the mixture were to be uniformly coloured, thedesired object would not be achieved, namely the formation of veiningimitating that of standard natural stone.

At the same time, as demonstrated by experimental tests, the colouredzones affect the entire thickness of the mixture, so that the predefinedobject of the invention is fully achieved.

The variant shown in FIG. 4 proposes the alternative solution ofmounting on the cross-member 36 an assembly with just a few colouringagent dispensing devices 38, said assembly 38 having, connected thereto,a drive system for controlled displacement thereof along thecross-member 36.

It is evident that a solution midway between those described above ispossible, namely one where a smaller number of dispensing devices 40 aremounted on the cross-member 36, with the each of them designed so thatit is movable along the cross-member over a limited distance, so as toensure more correct distribution of colouring agent on the surface ofthe mixture which is transported by the upper surface 32 of theextractor belt 30 towards the temporary support 14.

The product obtained fully satisfies the aforementioned requirements andhas the appearance shown in FIGS. 5 and 6 (where it is possible to see aslab with a toroidal edge and a slab with a semi-toroidal edge,respectively, the veining being visible throughout the thickness of theslab and therefore also along its edges).

Finally, it should be noted that with the present invention a furtheradvantage is achieved, mainly that of avoiding the need for any furtheroperation on the mixture already deposited on the temporary support (forexample using spiked tools) in order to ensure greater distribution ofthe colouring agent, with the obvious advantage in terms ofsimplification of the apparatus and the operating cycle.

It is understood that conceptually and mechanically equivalentmodifications and variations are possible and may be envisaged withoutdeparting from the scope of the present invention as defined in theaccompanying claims.

The invention claimed is:
 1. A method for manufacturing slabs having aveined effect imitating that of standard natural stone comprising:preparing at least one mixture, the mixture comprising a bonding agentand at least one granular product that comprises a stone or stone-likeor ceramic material having a specific particle size distribution;loading the at least one mixture into a metering/distributor unit thatcomprises a hopper and an extractor belt, the hopper having a top mouthfor loading the mixture and a bottom opening for discharging themixture, and the extractor belt having an upper surface that forms abottom of the hopper; transferring, by means of the extractor belt, theat least one mixture, having been loaded, to a downstream positionbeneath a dispensing device; dispensing at least one colouring orpigmenting agent from the dispensing device onto a surface of themixture that has been transferred to the downstream position, thedispensing resulting in a non-uniform distribution of the at least onecolouring or pigmenting agent on the surface of the mixture, the atleast one colouring or pigmenting agent being in solid or liquid form;further transferring, by means of the extractor belt, the mixture, whichhas the non-uniform distribution of the agent on the surface thereof, sothat the mixture free falls from the extractor belt to be distributed,in the form of a layer having a predetermined thickness, on a temporarysupport; subjecting the layer of mixture formed on the temporary supportto vibrocompression so as to obtain a rough-formed slab having an orderof thickness less than an order of length and width of the slab; andtransferring the rough-formed slab into a hardening station; wherein thestep of subjecting the layer of mixture to vibrocompression is carriedout under vacuum, while other steps of the method are carried out underatmospheric pressure; and wherein the further transferring of themixture so that the mixture free falls from the extractor belt resultsin the veining effect penetrating over an entire thickness of therough-formed slab.
 2. The method according to claim 1, wherein: thebonding agent of the at least one mixture comprises one of: an inorganicmaterial and a synthetic resin; the step of subjecting the layer ofmixture formed on the temporary support to vibrocompression is carriedout by a press, for a predetermined period of time, while a vibratorymovement of a pre-chosen frequency is applied to a ram of the press andthe layer formed on the temporary support is placed under the vacuum ofgiven intensity and subjected to the action of a press; and thehardening station subjects the transferred rough-formed slab to ahardening procedure that corresponds to the nature of the bonding agent.3. The method according to claim 1, further comprising: drying therough-formed slab following vibrocompression; and high-temperaturebaking the rough-formed slab following drying; wherein the bonding agentcomprises one of: clay and kaolin, and one of: sodium silicate and amixture of silicasol with polyvinyl alcohol.
 4. The method according toclaim 1, wherein dispensing the at least one colouring or pigmentingagent comprises dispensing the at least one colouring or pigmentingagent from a plurality of positions that are aligned transversely withrespect to a direction in which the extractor belt transfers the atleast one mixture.
 5. The method according to claim 1, wherein thecolouring or pigmenting agent comprises colouring or reflectivegranules.
 6. The method of claim 1, wherein the length and width of therough-formed slab is on the order of meters.
 7. The method of claim 6,wherein the rough-formed slab is obtained prior to using any sawingstep.
 8. The method of claim 6, wherein the thickness of therough-formed slab is on the order of millemeters.
 9. The method of claim8, wherein the rough-formed slab is obtained prior to using any sawingstep.
 10. The method of claim 1, wherein the dispensing of the at leastcolouring or pigmenting agent occurs intermittently, whereby a veiningeffect imitating that of standard natural stone is formed in therough-formed slab.
 11. The method of claim 10, wherein the dispending ofthe at least colouring or pigmenting agent occurs at irregular timeintervals.
 12. A method for manufacturing slabs having a veined effectimitating that of standard natural stone comprising: preparing at leastone mixture, the mixture comprising a bonding agent and at least onegranular product that comprises a stone or stone-like or ceramicmaterial having a specific particle size distribution; loading the atleast one mixture into a metering/distributor unit that comprises ahopper and an extractor belt, the hopper having a top mouth for loadingthe mixture and a bottom opening for discharging the mixture, and theextractor belt having an upper surface that forms a bottom of thehopper; transferring, by means of the extractor belt, the at least onemixture, having been loaded, to a downstream position beneath adispensing device; dispensing at least one colouring or pigmenting agentfrom the dispensing device onto a surface of the mixture that has beentransferred to the downstream position, the dispensing resulting in anon-uniform distribution of the at least one colouring or pigmentingagent on the surface of the mixture, the at least one colouring orpigmenting agent being in solid or liquid form; further transferring, bymeans of the extractor belt, the mixture, which has the non-uniformdistribution of the agent on the surface thereof, so that the mixturefree falls from the extractor belt to be distributed, in the form of alayer having a predetermined thickness, on a temporary support;subjecting the layer of mixture formed on the temporary support tovibrocompression so as to obtain a rough-formed slab having an order ofthickness less than an order of length and width of the slab, therough-formed slab obtained prior to using any sawing step; andtransferring the rough-formed slab into a hardening station; wherein thestep of subjecting the layer of mixture to vibrocompression is carriedout under vacuum, while other steps of the method are carried out underatmospheric pressure; and wherein the veining effect that results forthe rough-formed slab penetrates over an entire thickness of the slab.